1. Field of the Disclosure
The present patent document relates generally electronic control circuits for rare-earth-doped fiber amplifiers (“EDFA”) and more specifically to a control circuit for a multi-stage EDFA using a single programmable logic device (“PLD”).
2. Background of the Related Art
Use of fiber optics in the telecommunications industry to deliver data, such as television programming and high speed internet access, is becoming more prevalent. In order to transmit such data over long distances without undue signal deterioration fiber amplifiers are used. More specifically, multi-stage fiber amplifiers are used to boost the signal strength to sufficient power. Multi-stage fiber amplifiers include a first stage pump with one or more boosting stages. FIG. 1 shows a diagram of a prior art two-stage EDFA at 10. The first stage pump 12 boosts the signal to sufficient strength so that the second stage pump 14 does not introduce excess noise. Both pumps may include one or more diodes configured to pump an optical fiber. Power is supplied by a power supply 16. The amplification of the first stage pump 12 is controlled by a first gate 18. The amplification of the second stage pump is controlled by a second gate 20. Both gates 18, 20 may be field-effect transistors (or “FETs”).
However, this prior art technique of amplifying a signal suffers from a couple of disadvantages. Specifically, the power requirement of the second stage pump 14 is larger than power requirements of the first stage pump. As a consequence, the power supply 16 provides excess power that must be bled off of the first stage pump 12. This situation results in the requirement for enhanced cooling and heavier duty components, which significantly increase the cost of the fiber amplifier control circuit 10. Moreover, the FETs typically used as gates 18, 20 may fail causing the fiber amplifier control circuit 10 to malfunction.
Referring to FIG. 2, another prior art fiber amplifier control circuit is shown generally at 100. The second control circuit includes a first stage pump 102 and a second stage pump 104. Power is supplied by a power supply 106. The amplification of the first stage pump 102 is controlled by a first gate 108. The amplification of the second stage pump 104 is controlled by a second gate 110. Both gates 108, 110 may be a FET. Unlike the first prior art control circuit 10, the second prior art control circuit 100 includes a DC/DC power converter 112 connected between the power supply 106 and the first stage pump 102. The power converter 112 step-down the power from the power supply to an amount within tolerance for the first stage pump 102. As a consequence, the first gate 108 is operated within acceptable tolerances and risk of failure is averted.
However, this prior art solution is also not without its problems. The second control circuit 100 still requires two separate control inputs at the first and second gates 108, 110. These control inputs are provided by a microprocessor (not shown). Also, although the second control circuit 100 requires less robust components, the solution essentially shifts the costs to the requirement of an additional power supply with the inclusion of the converter 112.
Accordingly, it is desirable in the art to remove the need to use two PLD control circuits in multi-stage EDFAs.
It is also desirable to simplify power supply requirements and reduce processor load.